Process of manufacturing magnesium carbonate from magnesian limestone.



F. S. YOUNG. PROCESS OF MANUFAGTURING MAGNESIUM GAEBONATE FROM MAGNESIANLIMESTONE.

APPLICATION FILED OCT. 6, 1909.

Patented June 30, 1914.

UNITED STATES PATENT OFFICE.

FRANK S. YOUNG, OE NEWARK, NEW JERSEY.

PROCESS OF MANUFACTURING MAGNESIUM CARBONATE FROM MAGNESIAN LIMESTONE.

Specification of Letters Patent.

Patented June 30, 1914.

Application filed October 6, 1909. Serial No. 521,383.

This invention relates to processes for manufacturing magnesiumcarbonate from magnesian limestones, and particularly to such processesin which the magnesium compound is separated from the calcium bydissolving the former in water impregnated with carbon dioxid.

It is an improvement on the invention disclosed and claimed in myLetters Patent 734030, dated July 21st, 1903, in which the carbonationof the magnesium and calcium hydrates in suspension in water, isperformed at pressures equal to or approximating that of the atmosphere.In other words the carbon-dioxid-containin gas, used for thecarbonation, is contacte with the hydrates substantially uncompressed.

The object of my invention is the lowering of the cost of manufacture byeliminating a large part of the labor required in carrying out the oldintermittent process, and by eliminating the expense of compressing thecarbon dioxid bearing gas to the comparatively high pressures thereinused.

In the processof manufacture at present employed, the dolomite ordolimitic limestone is first burned in suitable kilns to a quicklime.This quicklime is next slaked and mixed with the proper proportion ofwater. It is then charged into strong iron carbonating tanks. The gasfrom the calcination of thevdolomite (which I will hereafter desi nateas kiln gas) is drawn from the kilns y a suitable compressor through anintermediate scrubber or cooler. The compressor compresses the gas to apressure of 4045 lb. per square inch in ordinary practice, after whichit passes through a suitable cooler. The cooled gas is then led to thebottom of the first of the carbonating tanks, passes through the milk oflime there in, leaves the tank through a suitable connection at the topand discharges at the bottom of the next tank in series, passes to thenext tank and so on through all the tanks that are being worked in theseries. The

spective carbonates. In the case 0 the car-' bonate of magnesium thissalt takes up an additional molecule of the carbon dioxid and forms,supposedly, a bicarbonate MgH, ((10 The existence of this salt has notbeen definitely proved in the solution and the existence of themagnesium in solution is sometimes explained as a simple solution of thecarbonate in carbon-dioxid impregnated water. The formation of thehypothetical salt MgH,(CO 'however, furnishes a convenient explanationof what takes place in the-carbonation of the calcium and magnesiumhydrates and I Will therefore assume that the solution. of the magnesiumdepends upon the formation of this salt. 0n this assumption, thereactions which take place in the carbonating tanks are If thecarbonation were carried far enough the calcium carbonate (in thepresenceof suficient water) would also be converted into a solublebicarbonate. It is the aim therefore to so conduct the carbonation thatthe gas is shut ofi from a tank at the point where the calcium justbegins to go into solution.

The milky liquid containing the bulk of the magnesium in solution as abicarbonate and the calcium in suspension as precipitated chalk, is nextfiltered. The clear filtrate containingthe magnesium in solution is nextboiled. This operation is preferably performed by blowing live steaminto the boiling tanks in contact with the entering stream ofbicarbonate liquor. By thus heating the bicarbonate solution thebicarbonate is broken up, the larger part of the CO, being driven 0%while the magnesium precipitates as an insoluble basic carbonate.

The temperature employed in boiling is usually about 205 to 212 Fah.

The temperature of boiling plays con: siderable part in determining thecomposition of the"precipitate,-the higher the temperature the morebasic the precipitate and the lower the proportion of the water ofcrystallization. The precipitated basic can 1W bonate is separated fromthe mother liquor in which it is suspended by filtration, and dried.

It has been heretofore thought that, in order to secure magnesiasolutions of workable strength, it was necessary to carbonate thecalcium and magnesium hydrates under high pressuresfrom 65 to 75 lb. persquare inch. Now I have discovered that .carbonate 1!) solutions ofmagnesia of workable strength may be obtained by contacting the hydratessuspended in water (milk of lime) with the CO bearing gas at atmosphericpressures. In present practice, the strength of the magnesia solutloncorresponds to 1.25 to 1.75% of basic carbonate. By my method I ameasily able to obtain solutions carrying a quantity of magnesiacorresponding to from 1.25 to 1.6% of basic carbonate. In carrying outmy process, I expose the hydrates suspended 1n water either in the formof a spray or rain or in a thin film to the action of the (XL-bearing,gas. I find that the suspended hydrates rapidly absorb the CO, to formcalcium carbonate and magnesium bicarbonate as in the present method. Inthe accompanying drawing I have shown one form of apparatus for applyingmy process.

Flgure 1 is a diagrammatic side elevation of the apparatus; Fig. 2 is across-section of one of the carbonatlng towers on the line 22 of Fig. 1showing a top-view of the ar-. rangement for distributing the liquor;Fig. 85 3 is a partial vertical section of the tower on the line 3-3 ofFi 2 showing the arrangement of the gri s; Fig. 4 is a view similar tothat of Fig. 3 but taken on the line l-A of Fig. 2 at right angles tothe line 40 3-3, showing the grids in side elevation.

1 represents the lime kiln. The dolomite lime from the kiln, whichchemically is a mixture of calcium and magnesium oxids, is slaked andmixed with an excess of water in the tanks 2, and is then pumped by theump 3 to the top of the first of a series 0 carbonating towers orchambers 4, 4', etc.

These carbonating towers may be built of light sheet iron supported on'a suitable frame work. Devices of any suitable kind such as layers ofcoarse broken dolomite supported on shelves-are provided in the interiorof the towers for keeping the descendin current of milk of lime brokenup into a ne rain or spray which should be uniformly distributed overthe cross-section of the tower. The form of filling employed may, ifpreferred, be a number of wooden grids superimposed upon each'other,vertically suspended curtains of burlap or almost any of the well knownarrangements used in gas scrubbing towers.

In the drawings I have shown partial sections throu h one form ofcarbonating e5 tower; but, it is, to be understood that I do not limitmyself to carrying out my process by the use of carbonating apparatus ofthis along t e bottom edge of the same to the walls. The mixture ofhydrates and water may be distributed to the uppermost grid by means ofa corresponding grid of perforated pipes, 16, of suitable size so setthat a pipe is vertically over each slat of the grid. Pipes 16 areconnected with'a cross-pipe, 17, which is connected with one of thepipes 18, 18, etc., according to the tower in which the grid issituated. The milky liquid drips from grid to grid in a great number offine streams, or as a rain, and thus exposes a large surface of contactwith the current of gas flowing through the tower. The carbonic acid inthe gas, is thus rapidly absorbed by the suspended hydrates, forming,firstly, carbonates and, secondly, bicarbonates if the exposure of theliquid to the action of carbonic acid is long enough continued. Themilky liquid dripping from the lowermost grid collects in the bottom ofthe tower and is pumped by one of the pumps 10 to the next tower.Instead of using a tower, if preferred, the carbonation may be performed in apparatus similar to the rotary scrubbers emp oyed in gasworks. Any carbonating apparatus which suflices to reduce the milkyliquid to a spray or rain or thin sheet and bring it into intimatecontact with the kiln gas will answer the purpose of my process. Thekiln gas is drawn off from the kiln through the pipe 5 and scrubber 6 tothe suction pipe 7 of compressor 8. From 8 the kiln gas passes throughthe cooler 9 to the bottom of the last section of the carbonatingapparatus. Passing through this it comes in contact with the most highlysaturated milk. Any residue of undissolved magnesium carbonate is thusexposed to the action of the strongest gas. The gas next passes throughthe rest of the carbonating apparatus in the reverse direction to thatfollowed by the circulation of the liquor. The weakest gas is thuscontacted with the caustic hydrates of the fresh liquor. From thecarbonating apparatus the milky liquid containing the magnesiumcarbonate in solution is pumped by a pump 10 to the filtering apparatus11. This filtering apparatus is preferably of some continuous type,although filter-presses of the ordinary type will answer. In thefiltering apparatus the undissolved constituents of the hydrates areseparated from the magnesia solution, which latter next passes to theboiler 12. Here it is heated by 7 working.

Having described my invention what ll claim is.:

1. The step in e manufacture of magnesium carbonate from magnesianlimestone, ,which comprises, exposing a finely divided mixture of thecalcined limestone andwater to the action of a s containing carbondioxid under a pressure not substantially above that of the atmosphere,to dissolve a major portion. of the maesia of said mixture in the waterof the mixture 2. The process of manufacturing magnesium carbonate,which comprises, calcining magnesian limestone to form a produet whichis capable of hydrating, slaking said product with water to convertoxide of calcium and 3 esium into hydrates, susending the so-ormedhydrates in water to orm a milky li uid, and contacting the said milkyliquid, w ile in a e state of subdivision, with uncompressed carbondioxid bearing gas under a pressure approximately equal to that of theatmosphere to dissolve magnesia of said lifiuid and to recipitate thecalcium of said iquid as car onate.

3. llhe process of manufacturing basicmagnesium carbonate, whichcomprises, calclning magnesian limestone to form a prodnot containingfree oxide of calcium and magnesium, slakin water to convert said oxideinto hyates, sus ending the- 'so-hydrated material in a su cientproportion of water to dissolve an amount of ma esium bicarbonateuivalent to the hy rated ma esia in sai material, reducing thesohydrated material and water to a e state of subdivison, subjecting theely suhdivided mixture to the action of substantially uncompressedcarbon-dioxid-bea v gas, derived from the calcination of sai limestone,under a pressure approximately equal to that of the atmosphere todissolve magnesia of said hydrated material to form a solution ofbicarbonate and precipitate the calcium of said material as carbonate,separating said carbonate of calcium from said magnesi m hicarbonatesolution, heating the separated hicarhonate solution to precipitate themagnesia therefrom as basic carbonate, and recovering said basiccarbonate.

Signed at New York, in the county of New York and State of New York,this 5th day of October A. D. 1909.

FRANK S. YQUNG.

Witnesses:

Louis F. Meant, W. J. nnnrm,

said material with ormed mixture of

